Leveraging Android Lint Checks

What is Android Lint?

• Android lint is a static analysis tool included in Android SDK and integrated within Android Studio. Available within Android Studio as warnings or run directly via gradle via lintDebug
• Lint checks are run directly within Android Studio on the fly, additional checks disabled by default such as library updates or thread usage analysis can be run by “Analyze->Run Inspection by Name”

Manually running named inspections

Why Lint

• Identify and correct issues prior to release
• Enforce custom rules, reduce on-boarding time for new engineers. Rather than document best practices, standards and gotchas just write a lint rule
• Library authors can ensure that library is being used correctly and any potential pitfalls are captured and reported directly to developers in IDE

Getting more from Lint

• Many integration are disabled by default. Check disabled inspections (Editor->Inspections). For example Java/Kotlin interop inspections are disabled by default
• Integrate with CI
• Setup a baseline to ignore all existing issues, fail only on new issues
• Add custom lint checks for your project either directly in app or include in library aar. Custom lint checks can check java/kotlin source, xml files such as layouts, AndroidManifest and gradle files. Custom lint checks included in aar will automatically be applied to apps that consume the library

Custom Lint Checks: Overview

All custom lint checks will have the following components:

Specification

• Specify unique identifier, description, category, priority and severity
• Specify unique lint check within the IssueRegistry
• Example: LogWtfUsage

Filter

• What should lint check be applied to? Lint check can be filtered to evaluate specific methods, classes, annotations, import statements
• Example: Identify all methods named wtf

Evaluation and Report

• Perform any additional analysis such as checking package names, evaluating children
• If issue is identified report issue details along with optional metadata for quickfix

Custom Lint check with suggested replacement in Android Studio

Custom Lint Checks: Setup

• Create new module that will contain the source of the custom lint checks
• Lint checks can be applied directly to app implementation lintChecks(project(":mylintchecks")) or in included in an aar lib module implementation lintPublish(project(":mylintchecks"))
• Add custom lint checks to the IssueRegistry
• See Google Sample or Sample Project

lint check module build.gradle

Issue Registry

Recipe: Find usages of a method and suggest replacement

Identify and replace all usages of android.util.Log.wtf, notify user and allow them to apply a quickfix replacement Log.f

Recipe Deprecate Libraries

One of the libraries in use has been deprecated. Since we don’t own the code we cannot use the @Deprecated annotation but would like to avoid new usages. Identify and report all usages of MyDeprecatedLibClass()

Testing

Lint framework provides some utilities in the form of a builder pattern to test lint checks. The easiest way to debug and build a lint test is often to build an associated test.

Further Reading

• PSI Viewer
• Android Lint Checks
• Lint Dev Group
• Jetbrains PSI Reference Guide